In general, the processing of black-and-white silver halide photographic elements is performed in the sequence of development, fixing and washing. Development is commonly carried out with aqueous alkaline developer compositions containing a developing agent of the dihydroxybenzene type, such as hydroquinone. Usually, dihydroxybenzene developing agents are used in combination with auxiliary superadditive developing agents. As explained in Mason, Photographic Processing Chemistry, Focal Press, London, 1975, "superadditivity" refers to a synergistic effect whereby the combined activity of a mixture of two developing agents is greater than the sum of two activities when each agent is used alone in the same developing solution. "Superadditivity" is especially described on pages 29 and 103 of Mason. Examples of useful auxiliary superadditive developing agents are 3-pyrazolidones, such as 1-phenyl-3-pyrazolidone (Phenidone) and 1-phenyl4,4-dimethyl-3-pyrazolidone (Dimezone), and aminophenols, such as p-methylaminophenol sulfate (Metol). Generally, the combinations of developing agents showing superadditivity consist of one developing agent from the dihydroxybenzene type (hydroquinone) and one developing agent from either the aminophenol type or the 3-pyrazolidone type. There is a case reported at page 29 of Mason in which one of the developing agent is not of the dihydroxybenzene type, that is the case of the Phenidone/Glycin system which, however, has proved of poor utility.
While development processes based on the use of hydroquinone generally provide very good sensitometric results, they are disadvantageous with regard to ecological and environmental considerations. In particular, hydroquinone and its derivatives, and the oxidized forms thereof, have become of increasing concern in recent years from the point of view of potential toxicity and environmental pollution. Thus, there is an urgent need in the art for a hydroquinone-free development process which produces the same good results as the known development process containing hydroquinone, but which is environmentally more friendly.
Developing solutions free of hydroquinone and using ascorbic acid derivatives as developing agents have been used heretofore in a wide variety of photographic developing processes. Thus, for example, developing compositions containing ascorbic acid developing agents have been disclosed in U.S. Pat. Nos. 2,688,548; 2,688,549; 3,922,168; 3,942,985; 4,168,977; 4,478,928; 4,650,746 and 4,975,354.
However, developing compositions containing ascorbic acid derivatives have poor resistance against aerial oxidation and cannot be left in continuous transport automatic processors for several days without undergoing a dramatic decrease of developing activity. Recently, several attempts have been made to increase resistance against aerial oxidation of developing compositions containing ascorbic acid derivatives as developing agents. U.S. Pat. No. 5,098,819 describes a photographic developer composition comprising a developer selected from the group consisting of ascorbic acid and its sugar-type derivatives, their salts and mixture thereof, together with a sulfite, an alkali metal carbonate and a 3-pyrazolidone developer compound.
U.S. Pat. No. 5,147,767 discloses an environmentally-safe, non-toxic non-hydroquinone and non-alkali metal hydroxide containing photographic developer composition comprising a developer selected from the group consisting of 2-keto gluconic acid and derivatives thereof, together with a sulfite, an alkali metal carbonate and a 3-pyrazolidone developer compound.
WO 93-11,456 discloses a system for rapid access processing of photographic silver halide elements comprising, in combination, a photographic silver halide element of the type containing a hydrazine compound and a developer solution comprising at least one ascorbic acid developing agent selected from the group consisting of ascorbic acid, derivatives thereof and salts of either.
U.S. Pat. No. 5,236,816 describes a photographic developing solution which is free of dihydroxybenzene developing agents, has a pH in the range of from 9.5 to 11.5 and comprises (1) and ascorbic acid developing agent, (2) an auxiliary super-additive developing agent and (3) a carbonate buffering agent in a concentration of at least 0.5 molar. The developing solution is particularly useful in a process for forming a high contrast image in the graphic arts field utilizing a silver halide photographic element comprising a hydrazine compound which functions as a nucleating agent and an amino compound which functions as an incorporated booster. The developing solution is not particularly useful when a non-nucleated film, for example a radiographic film must be developed.
EP 573,700 discloses a process for developing a silver halide photographic material in a continuous automatic way using a developer solution containing an ascorbic acid analogue or derivative and a 3-pyrazolidone derivative as developing agents and replenishing the developer solution with a replenishing composition having a defined pH.
Developing compositions containing ascorbic acid as primary developing agent have the advantage of providing an environmentally favorable alternative to the use of developing solutions containing dihydroxybenzene developing agents. However, the attempts to improve resistance to aerial oxidation of the developing compositions containing ascorbic acid derivatives as primary developing agent do not sufficiently inhibit the pH decrease of the composition. In fact, as a consequence of oxidation, a gradual pH decrease will always occur, which in turn lowers the developing activity with a dramatic decrease in sensitivity and gradation for a given constant development time, especially when said developing compositions are used in continuous transport automatic processors for several days. In addition, another disadvantage of the developing compositions is that they are useful in the graphic arts film when a high contrast image is to be obtained, but they are not useful in the radiographic field, where a high contrast image is not desired.
It is object of the present invention to provide a black-and-white developing composition, useful both in graphic arts and radiographic fields, free of dihydroxybenzene developing agent, being stable against aerial oxidation and giving very constant processing results during automatic continues processing.